The months of April and May are best known for waterfalls. Snowmelt is starting to come off the mountains, and results in cascades of water tumbling down the cliffs. It's a little too early for spring flowers and roads are often still closed, or require chains.
Temperatures range in the 60s and low 70s, but the occasional winter storm can still pass through, dumping a layer of snow over everything.
June through September is the most exuberant period to experience the park. The waterfalls run until August, the wildflowers come out of their winter shells, the grass is green, the animals are out foraging and ... the park is full of other visitors as well. It's a great time to visit, even with the crowds.
Yosemite Park weather heats up to the 80s and mid-90s during summer, which can be a little uncomfortable for some people. There are thunderstorms only occasionally.
October and November are great months to visit Yosemite. The entire park is open, but the throngs of summer visitors are gone, leaving the park vulnerable to quiet exploration. The waterfalls will slow to trickles, if running at all, but mid-October brings bright splashes of color from the maples, oaks and dogwoods.
Temperatures vary considerably, but are generally around upper 50s to lower 70s. Bring layers to help keep warm as the temperature rises in the day, then cools off after the sun goes down.
The winter months of December to March are a fantastic time to visit. The park is a quiet haven, with cross country ski trails accessing winter huts, and the Badger Pass Ski Area open for operation. Hikes in Yosemite Valley generally stay open as well. Come to enjoy the peace and calm of an quiet park.
During winter, the Yosemite weather forecast could change everyday: snow, sun, clouds, and then back. Temperatures stay around 40s and 50s during the day. The bulk of precipitation comes in the winter months, so always be prepared for snow.
Throughout the Year
Yosemite has a great deal of elevation change within the park. The higher elevations in the park will be considerably colder than in the valley. For Tuolumne Meadows, for instance, subtract 10°F to 20°F from the average temperatures given.
Sturdy shoes are a good idea as well. Mist from the waterfalls can make rocks slippery, and patches of ice can remain well into June or July.